a) Field of the Invention
This invention relates to dyestuffs, which play an important role in color filters for display devices such as liquid crystal television sets and also in color separation filters for image pickup tubes, color copiers, video printers and the like.
b) Description of the Related Art
Conventionally known dyestuffs for filters include, as blue dyestuffs, anthraquinone dyestuffs (Japanese Patent Laid-Open Nos. 136604/1987 and 197459/1987) and triphenylmethane dyestuffs ("1990s Development and Market Trend of Special Functional Dyestuffs", 47-48, CMC Co., Ltd.); as red dyestuffs, anthraquinone dyestuffs (Japanese Patent Laid-Open No. 74960/1987), azo dyestuffs ("1990s Development and Market Trend of Special Functional Dyestuffs", 47, CMC Co., Ltd.) and perinone dyestuffs (Japanese Patent Laid-Open No. 136606/1987); as green dyestuffs, anthraquinone dyestuffs (Japanese Patent Laid-Open No. 246258/1986), triphenylmethane dyestuffs ("1990s Development and Market Trend of Special Functional Dyestuffs", 47-48, CMC Co., Ltd.), phthalocyanine dyestuffs (Japanese Patent Laid-Open Nos. 249102/1985, 140902/1986, 254903/1986, 254904/1986, 6904/1989, 88505/1989, and 233401/1989), perinone dyestuffs (Japanese Patent Laid-Open No. 136606/1987), and naphthoquinone dyestuffs (Japanese Patent Laid-Open No. 268761/1986); and as yellow dyestuffs, azo and vat-dye pigments ("1990s Development and Market Trend of Special Functional Dyestuffs", 48, CMC Co., Ltd.) and water-soluble azo dyes (Japanese Patent Laid-Open Nos. 204010/1984 and 204011/1984).
As to the blue dyestuffs, the anthraquinone compounds do not permit sufficient light transmission around 440 nm but have high transmittance at wavelengths of 500 nm and longer, so that they have a broad transmittance curve. In the case of the triphenylmethane dyestuffs, their molecules are in an ionized form so that they are suited for coloring filters making use of gelatin or casein as a substrate and were hence used in gelatin-type filters. Those filters themselves however had low light fastness and heat resistance. Turning next to the red dyestuffs, the anthraquinone compounds and perinone compounds are accompanied by the drawback that they have low transmittance and poor color visibility, although their durability is good. The azo compounds are water-soluble and are thus suited for coloring filters making use of gelatin or casein as a substrate. The azo compounds were therefore employed in gelatin-type filters. Due to poor heat and moisture resistance of the filters themselves, their applications were limited. Further, for poor light fastness, heat resistance and moisture resistance of the dyestuffs themselves, the filters were not usable in general devices. Among the green dyestuffs, sulfo-containing phthalocyanine compounds which are water-soluble compounds are suited in coloring filters making use of gelatin or casein as a substrate and were hence used in gelatin-type filters. Their applications were however limited due to poor heat and moisture resistance of the filters themselves. Further, the anthraquinone and naphthoquinone dyestuffs do not permit sufficient transmission for light of 500-600 nm and their light fastness is not sufficient. In the case of the triphenylmethane dyestuffs, their molecules are in an ionized form so that they are suited for coloring filters making use of gelatin or casein as a substrate and were hence used in gelatin-type filters. Those filters themselves however had poor heat and moisture resistance so that a limitation was imposed on their applications. In addition, due to poor light fastness, heat resistance and moisture resistance of the dyestuffs themselves, they were not usable in general display devices. Dealing finally with the yellow dyestuffs, the azo pigments and vat dyes are used for the fabrication of filters by the pigment dispersion method. Although filters obtained by the pigment dispersion method have high pattern accuracy and excellent heat resistance and light fastness, they are accompanied by the following drawbacks:
(1) Due to scattering of light by pigment particles, the filters have inferior light transmittance and poor contrast. PA1 (2) Prior to coating a photosensitive resin in which a pigment is uniformly dispersed, it is necessary to eliminate dirt and large particles by causing the photosensitive resin to pass through a screen, leading to potential problems, for example, troubles in the fabrication process such as screen clogging due to agglomeration of pigment particles.
The water-soluble azo dyes are used for the fabrication of filters by the dyeing method. Color filters obtained by the dyeing method are excellent in pattern resolution, dimensional accuracy and light transmission and also high in color lightness. They are however accompanied with the drawback that their heat resistance is insufficient for their use of gelatin or casein as a photosensitive resin.